April 30, 2014 AT 2:00 am

Striker: Real-time Cadence Wearable #WearableWednesday

Brian from San Francisco creative agency Manifold sent in this great project from their lead technologist who is an avid triathlete.

They often say the best projects are those that scratch a personal itch. At Manifold we are a passionate bunch. Our personal passions often bleed into the work we do and our latest pet project is no exception. I’ve spent the better part of the last 5 years training for one endurance event or another. Mostly cycling, but this year I’m focused on triathlons, specifically Ironman. This has meant a lot more running than in past years (about 800 miles so far and counting). Along the way I’ve read more articles on proper running form than I can recall. One constant theme jumps out over and over again; cadence (a.k.a.) stride rate, revolutions per minute (rpm), leg turnover, etc. Studies of elite athletes have shown that a faster cadence leads to increased speed and endurance as well as less injury caused by things like over-striding. Many articles quote a magic cadence number of 180 strides per minute (90 per foot) as being the perfect target. This comes from Daniels’ Running Forumla, a book written by legendary distance running coach Jack Daniels. The 180 target is not without debate. Some would say that’s the minimum and others would say the number is dependent on the unique physical characteristics of each athlete. So while everyone may not agree on the number most would agree that cadence is important. You should understand what your cadence is and work to improve it. Lets put aside the debate on what the number should be and focus on how we measure our cadence. After all, if we can measure it then we can improve it.

There are plenty of devices aimed at measure cadence on a bike. Most commonly it is a simple magnet attached to the wheel with another stationary part that sits on the bike frame. The bike computer tracks the number of times the magnet passes the stationary part per minute. Unfortunately, in the running world devices like these are not so common. Most good running watches are capable of tracking cadence with the addition of a footpod device. However, the vast majority fail to display this information in real-time. If they do track cadence then most often they only expose the average cadence or provide an alarm feature that triggers when you are above or below a user defined threshold. Average cadence is great for reviewing you run after the fact, but what about being able to adjust your cadence in real-time. The longer your run the harder it is to move the average. In the perfect world what you’d have is real-time cadence during the run and an average after the run. Imagine you just returned from a 2+ hour run and upon review realize that your cadence was way too low. Too late to do anything about it. Better luck next time! Some would suggest you manually count the number of steps taken with 1 foot for a minute and multiple that by 2. Others suggest using a metronome or an MP3 to help keep you on track. Try doing any of those on a multi-hour run day after day and you’ll drive yourself crazy. There has to be a better way and that is the real point of this post. We’ve been known to dabble in hardware hacking from time to time and have been looking for a reason to explore the world of wearable computing for a while. We decided to prototype a hardware device that was capable of tracking real-time running cadence. Our name for this device is Striker. The rest of this post will focus on how we built Striker and how you can take and learn from what we’ve done. We’ve open-sourced all the code, 3D models, and provided fritzing sketches for the hardware wiring. You’ll find links for all of these at the end of the post.

Featured Adafruit Products!

>Adafruit 0.56″ 4-Digit 7-Segment Display w/I2C Backpack – Blue: What’s better than a single LED? Lots of LEDs! A fun way to make a small display is to use an 8×8 matrix or a 4-digit 7-segment display. Matrices like these are ‘multiplexed’ – so to control all the seven-segment LEDs you need 14 pins. That’s a lot of pins, and there are driver chips like the MAX7219 that can control a matrix for you but there’s a lot of wiring to set up and they take up a ton of space. Here at Adafruit we feel your pain! After all, wouldn’t it be awesome if you could control a matrix without tons of wiring? That’s where these adorable LED matrix backpacks come in. We have them in two flavors – a mini 8×8 and a 4-digit 0.56″ 7-segment. They work perfectly with the matrices we stock in the Adafruit shop and make adding a bright little display trivial. Read more.

Monochrome 128×32 SPI OLED graphic display: These displays are small, only about 1″ diagonal, but very readable due to the high contrast of an OLED display. This display is made of 128×32 individual white OLED pixels, each one is turned on or off by the controller chip. Because the display makes its own light, no backlight is required. This reduces the power required to run the OLED and is why the display has such high contrast; we really like this miniature display for its crispness! Read more.

Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, or even use Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for MakeCode, CircuitPython, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.